The International Regulations for Preventing Collisions at Sea 1972 (Colregs) are published by the International Maritime Organization (IMO) and set out, among other things, the "rules of the road" or navigation rules to be followed by ships and other vessels at sea to prevent collisions between two or more vessels.[1][2] COLREGs can also refer to the specific political line that divides inland waterways, which are subject to their own navigation rules, and coastal waterways, which are subject to international navigation rules. The COLREGs are derived from a multilateral treaty called the Convention on the International Regulations for Preventing Collisions at Sea.

Although rules for navigating vessels inland may differ, the international rules specify that they should be as closely in line with the international rules as possible. In most of continental Europe, the Code Européen des Voies de la Navigation Intérieure (CEVNI, or the European Code for Navigation on Inland Waters) apply. In the United States, the rules for vessels navigating inland are published alongside the international rules.[3]

Prior to the development of a single set of international rules and practices, there existed separate practices and various conventions and informal procedures in different parts of the world, as advanced by various maritime nations. As a result, there were inconsistencies and even contradictions that gave rise to unintended collisions. Vessel navigation lights for operating in darkness as well as navigation marks also were not standardised, giving rise to dangerous confusion and ambiguity between vessels at risk of colliding.

With the advent of steam-powered ships in the mid-19th century, conventions for sailing vessel navigation had to be supplemented with conventions for power-driven vessel navigation. Sailing vessels are limited as to their manoeuvrability in that they cannot sail directly to windward or into the eye of the wind and cannot be readily navigated in the absence of wind. On the other hand, steamships can manoeuvre in all 360 degrees of direction and can be manoeuvred irrespective of the presence or absence of wind.

In 1840 in London, the Trinity House drew up a set of regulations which were enacted by Parliament in 1846. The Trinity House rules were included in the Steam Navigation Act of 1846, and the Admiralty regulations regarding lights for steam ships were included in this statute in 1848. In 1849 Congress extended the light requirements to sailing vessels on US waters. In the UK in 1858 coloured sidelights were recommended for sailing vessels and fog signals were required to be given, by steam vessels on the ships whistle and by sailing vessels on the fog horn or bell, while a separate but similar action was also taken in the United States

In 1863 a new set of rules drawn up by the British Board of Trade, in consultation with the French government, came into force. By 1864 the regulations (or Articles) had been adopted by more than thirty maritime countries, including Germany and the United States (passed by the United States Congress as Rules to prevent Collisions at Sea. An act fixing certain rules and regulations for preventing collisions on the water. 29 April 1864, ch. 69.[4] and signed into law by President Abraham Lincoln).

In 1867, Thomas Gray, assistant secretary to the London Maritime Department of Trade, wrote The Rule of the Road, a pamphlet that became famous for its well-known mnemonic verses.

In 1880, the 1863 Articles were supplemented with whistle signals and in 1884 a new set of international regulations was implemented.

In 1889 the United States convened the first international maritime conference in Washington, D.C. The resulting rules were adopted in 1890 and effected in 1897. Some minor changes were made during the 1910 Brussels Maritime Conference and some rule changes were proposed, but never ratified, at the 1929 International Conference on Safety of Life at Sea (S.O.L.A.S.) With the recommendation that the direction of a turn be referenced by the rudder instead of the helm or tiller being informally agreed by all maritime nations in 1935.

The 1948 S.O.L.A.S. International Conference made several recommendations, including the recognition of R.A.D.A.R., these were eventually ratified in 1952 and became effective in 1954. Further recommendations were made by a S.O.L.A.S. Conference in London in 1960 which became effective in 1965

The International Regulations for Preventing Collisions at Sea were adopted as a Convention of the International Maritime Organization on 20 October 1972 and entered into force on 15 July 1977. They were designed to update and replace the Collision Regulations of 1960, particularly with regard to Traffic Separation Schemes (TSS) following the first of these, introduced in the Strait of Dover in 1967.[1] As of June 2013, the Convention has been ratified by 155 states representing 98.7 per cent of the tonnage of the world's merchant fleets.[5]

They have been amended several times since their first adoption. In 1981 Rule 10 was amended with regard to dredging or surveying in traffic separation schemes. In 1987 amendments were made to several rules, including rule 1(e) for vessels of special construction; rule 3(h), vessels constrained by her draught and Rule 10(c), crossing traffic lanes. In 1989 Rule 10 was altered to stop unnecessary use of the inshore traffic zones associated with TSS. In 1993 amendments were made concerning the positioning of lights on vessels. In 2001 new rules were added relating to wing-in-ground-effect (WIG) craft and in 2007 the text of Annex IV (Distress signals) was rewritten.[1]

Each country that is a member of the International Maritime Organization (IMO) designates an "Administration" or federal authority or agency for implementing the provisions of the COLREG convention as it applies to vessels over which the federal authority has jurisdiction. In other words, the IMO convention including the almost four dozen "rules" contained in the international regulations is adopted by each member country signatory to the convention. Each national or federal administration is responsible for the implementation and enforcement of the regulations as it applies to ships and vessels over which it has legal authority. For example, the US Coast Guard regulates US vessels, while Transport Canada regulates Canadian vessels. In effect, there is a set of national navigation laws (regulations) which conform to the international convention. Each administration is empowered to enact modifications that apply to vessels in waters under the national jurisdiction concerned, provided that any such modifications are not inconsistent with the COLREGs.

The full text of the current rules is available from various national administration websites. Typically, the COLREGs are incorporated within national regulatory instruments "by reference". There are multiple books in many languages that not only provide the rules, but also provide discussion and examples related to interpreting the raw rules, including diagrams and hypothetical cases. The UK version is provided by the Maritime and Coastguard Agency (MCA).[6] The COLREGs are contained within the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations of 1996 as amended from time to time and is distributed and accessed in the form of a "Merchant Shipping Notice" (MSN), which is used to "convey mandatory information that must be complied with under UK legislation. These MSNs relate to Statutory Instruments and contain the technical detail of such regulations."[7] The MCA says that material it publishes is subject to Crown copyright protection, which means that it may be reproduced free of charge in any format or medium for research or private study, provided it is reproduced accurately and not used in a misleading context.[8] The summary below is based upon but is not identical to the published text.[9]

The rules are specified in great detail in the regulations. Certain individuals are legally required to carry or possess a copy of the rules, such as the owners and/or operators of certain vessels. COLREG laws exist within each maritime jurisdiction. Any individual subject to such requirements should be aware of the complete, official wording. Copies are available from government and official sources, such as the coast guard.

In addition to the actual rules, a body of legal precedents and case law exists; judgements on the application of the various rules with respect to specific legal and admiralty court cases have been published. Such precedents of judicial interpretation provide guidance as to how the rules were deemed to have applied given specific facts, often with a view to apportioning contributory liability or blame.

A commonly held misconception concerning the rules of marine navigation is that by following specific rules, a vessel can gain certain rights of way over other vessels. No vessel ever has absolute "right of way" over other vessels. Rather, there can be a "give way" (burdened) vessel and a "stand on" (privileged) vessel, or there may be two give way vessels with no stand on vessel. A stand on vessel does not have an absolute right of way over any give way vessel, for if there is a risk of collision, a stand on vessel may still be obliged under Rule 2 to give way so as to avoid it, if doing so will be effective and is practicable. Two power-driven vessels approaching each other head to head, are both deemed to be "give way" and both are required to alter course so as to avoid colliding with the other. Neither vessel has "right of way".

(a) These rules shall apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels.

(b) Nothing in these Rules shall interfere with the operation of special rules made by an appropriate authority for roadsteads, harbours, rivers, lakes, or inland waterways connected with the high seas and navigable by seagoing vessels. Such special rules shall conform as closely as possible to these Rules.

(c) Nothing in these Rules shall interfere with the operation of any special rule made by the government of any State with respect to additional station or signal lights, shapes or whistle signals for ships of war and vessels proceeding under convoy, or with respect to additional station or signal lights or shapes for fishing vessels engaged in fishing as a fleet. These additional station or signal lights, shapes or whistle signals shall, so far as possible, be such that they cannot be mistaken for any light, shape, or signal authorised elsewhere under these Rules

(d) Traffic separation schemes may be adopted by the Organization for the purpose of these Rules.

(e) Whenever the Government concerned shall have determined that a vessel of any special construction or purpose cannot comply with the provisions of any of these Rules with respect to the number, position, range, or arc of visibility of lights or shapes, as well as to the disposition and characteristics of sound-signalling appliances, such vessel shall comply with such other provisions in regard to the number, position, range or arc of visibility of lights or shapes, as well as to the disposition and characteristics of sound-signalling appliances, as her Government shall have determined to be the closest possible compliance with these Rules in respect of that vessel.

2. Responsibility

(a) Nothing in these Rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case

(b) In construing and complying with these rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these rules necessary to avoid immediate danger

[Rule 2 is sometimes referred to as the "General Prudential" rule and provides for non-conformance with stated rules to prevent a collision, because what is paramount is to avoid or minimise the damaging effects of a collision, as opposed to blindly following the rules to the letter. The overall intent is to minimise actual collision taking place rather than rule compliance in and of itself, per se.]

3. General Definitions

For the purpose of these Rules, except where the context otherwise requires:

(b) The term "power-driven vessel" means any vessel propelled by machinery.

(c) The term "sailing vessel" means any vessel under sail provided that propelling machinery, if fitted, is not being used.

(d) The term "vessel engaged in fishing" means any vessel fishing with nets, lines, trawls or other fishing apparatus which restrict manoeuvrability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict manoeuvrability.

(e) The word "seaplane" includes any aircraft designed to manoeuvre on the water.

(f) The term "vessel not under command" means a vessel which through some exceptional circumstance is unable to manoeuvre as required by these Rules and is therefore unable to keep out of the way of another vessel.

(g) The term "vessel restricted in her ability to manoeuvre" means a vessel which from the nature of her work is restricted in her ability to manoeuvre as required by these Rules and is therefore unable to keep out of the way of another vessel. The term "vessels restricted in their ability to manoeuvre" shall include but not be limited to:

(i) a vessel engaged in laying, servicing, or picking up a navigation mark, submarine cable or pipeline;

(ii) a vessel engaged in dredging, surveying or underwater operations;

(iii) a vessel engaged in replenishment or transferring persons, provisions or cargo while underway;

(iv) a vessel engaged in the launching or recovery of aircraft;

(v) a vessel engaged in mine clearance operations;

(vi) a vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course.

(h) The term "vessel constrained by her draught" means a power-driven vessel which, because of her draught in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following.

(i) The word "underway" means that a vessel is not at anchor, or made fast to the shore, or aground.

(j) The words "length" and "breadth" of a vessel mean her length overall and greatest breadth.

(k) Vessels shall be deemed to be in sight of one another only when one can be observed visually from the other.

(l) The term "restricted visibility" means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or other similar causes.

(m) The term "Wing-In-Ground (WIG) craft" means a multimodal craft which, in its main operational mode, flies in close proximity to the surface by utilising surface-effect action.

The rules apply in any condition of visibility (e.g., in sight or in restricted visibility).

5. Look-out

Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.

6. Safe speed

Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.

In determining a safe speed the following factors shall be among those taken into account:

(a) By all vessels:

(i) the state of visibility;

(ii) the traffic density including concentrations of fishing vessels or any other vessels;

(iii) the maneuvrability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions;

(iv) at night the presence of background light such as from shore lights or from back scatter of her own lights;

(v) the state of wind, sea and current, and the proximity of navigational hazards;

(vi) the draught in relation to the available depth of water.

(b) Additionally, by vessels with operational radar:

(i) the characteristics, efficiency and limitations of the radar equipment;

(ii) any constraints imposed by the radar range scale in use;

(iii) the effect on radar detection of the sea state, weather and other sources of interference;

(iv) the possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;

(v) the number, location and movement of vessels detected by radar;

(vi) the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.

7. Risk of Collision

Vessels must use all available means to determine the risk of a collision, including the use of radar (if available) to get early warning of the risk of collision by radar plotting or equivalent systematic observation of detected objects. (e.g. ARPA, AIS).

If the distance of any vessel is reducing and her compass bearing is not changing much or it is a large vessel or towing vessel at close distance, or if there is any doubt, then a risk of collision shall be deemed to exist.[6]

Ships must cross traffic lanes steering a course "as nearly as practicable" at right angles to the direction of traffic. This reduces confusion and enables that vessel to cross the lane as quickly as possible.

Vessel entering a traffic separation scheme should do it at an angle as small as practicable.

A traffic separation scheme does not relieve any vessel from complying with other rules.

The following rules 11–18 applies to vessels in sight of one another. (Section III has specific requirements for restricted visibility)

12. Sailing vessels

Two sailing vessels approaching one another must give-way as follows:

Port gives way to Starboard. When each has the wind on a different side, the vessel which has the wind to port must give way;

Windward gives way to leeward. When both have the wind on the same side, the vessel which is windward must give way to the vessel which is leeward;

Unsure port gives way. If a vessel, with the wind on the port side, sees a vessel to windward and cannot determine whether the other vessel has the wind on the port or the starboard side, they must give way.

13. Overtaking

An overtaking vessel must keep out of the way of the vessel being overtaken. "Overtaking" means approaching another vessel at more than 22.5 degrees abaft[10] her beam, i.e., so that at night, the overtaking vessel would see only the stern light and neither of the sidelights of the vessel being overtaken.[6]

14. Head-on situations

When two power-driven vessels are meeting head-on both must alter course to starboard so that they pass on the port side of the other. "Head-on" means seeing the other vessel ahead or nearly ahead so that by night her masthead lights are actually or nearly lined up and/or seeing both her sidelights, or by day seeing a similar aspect of her.[6] "If you see three lights ahead, starboard wheel and show your red."

15. Crossing situations

When two power-driven vessels are crossing, the vessel which has the other on the starboard side must give way and avoid crossing ahead of her.[6] The saying is "If to starboard red appear, 'tis your duty to keep clear".[11] "...Act as judgement says is proper: port or starboard, back or stop her."

16. The give-way vessel

The give-way vessel must take early and substantial action to keep well clear.[6]

17. The stand-on vessel

The stand-on vessel shall maintain her course and speed, but she may take action to avoid collision if it becomes clear that the give-way vessel is not taking appropriate action, or when so close that collision can no longer be avoided by the actions of the give-way vessel alone. In a crossing situation, the stand-on vessel should avoid turning to port even if the give-way vessel is not taking appropriate action. These options for the stand-on vessel do not relieve the give-way vessel of her obligations under the rules.[6]

a vessel restricted in her ability to manoeuvre (this may include vessels towing one another[12]);

a vessel engaged in fishing;

a sailing vessel.

A sailing vessel must give way to:

a vessel not under command;

a vessel restricted in her ability to manoeuvre;

a vessel engaged in fishing.

A vessel engaged in fishing when underway shall, so far as possible, keep out of the way of:

a vessel not under command;

a vessel restricted in her ability to manoeuvre.

Any vessel other than a vessel not under command or a vessel restricted in her ability to manoeuvre shall, if possible, not impede the safe passage of a vessel constrained by her draft, exhibiting the signals in Rule 28.

A vessel constrained by her draft shall navigate with particular caution having full regard to her special condition.[6]

(a) Rule 19 applies to vessels (not in sight of one another) in or near restricted visibility.

(b) All ships shall proceed at a safe speed for the condition of visibility (see Rule 6). A power-driven vessel shall have her engine(s) on stand-by for immediate maneuver.

(c) All ships shall comply with Section I of this Part e.g., Rules 5 (lookout), 6 (safe speed), 7 (risk of collision), 8 (action to avoid collisions), 9 (narrow channels), and 10 (TSS) with due regard for the visibility conditions.

(d) If another vessel is detected by radar alone, and a close-quarters or collision risk is suspected, a vessel should take early and substantial action to avoid the other, but:

(i) avoid any turn to port for a vessel detected forward of the beam, except for a vessel being overtaken,

(ii) avoid any change of course toward a vessel abeam or abaft the beam.

When the fog signal of another vessel is heard, apparently forward of the beam, a vessel should reduce speed to the minimum at which she can maintain her course, or if necessary stop, and navigate with extreme caution until there is no risk of collision.[6]

Rules concerning lights apply from sunset to sunrise, in conditions of restricted visibility, and in all other circumstances when it is deemed necessary. Rules concerning shapes apply during the day.[6]

21. Definitions

"Masthead light" means a white light on the centreline of the vessel showing from right ahead to 22.5 degrees abaft the beam on either side of the vessel.

"Sidelights" means a green light on the starboard side and a red light on the port side each showing from right ahead to 22.5 degrees abaft the beam on its respective side. If the vessel is less than 20 metres (66 ft) long, the sidelights may be combined in one fixture carried on the centreline of the vessel.

"Sternlight" means a white light placed as nearly as practicable at the stern showing 67.5 degrees from right aft on each side of the vessel.

"Towing light" means a yellow light having the same characteristics as a "sternlight" defined above.

"All-round light" means a light visible from 360 degrees of the horizon.

If over 50 metres (164 ft) length, then also a second masthead light aft and higher than the forward one; except that a vessel of less than 50 metres in length shall not be obliged to exhibit such light but may do so;

sidelights;

a sternlight.

A hovercraft must also display an all-round flashing yellow light.

A wing-in-ground craft must also display a bright all-round flashing red light when taking off, landing, or flying near the surface.

A power-driven vessel of less than 12 metres (39.4 ft) may display only an all-round white light and sidelights. However, in the case of a skiff a wooden clinker rowing boat which falls into this category only needs to be capable of showing a white light.

A power-driven vessel of less than 7 metres (23.0 ft) whose maximum speed does not exceed 7 knots (13 km/h; 8 mph) must be capable of showing a white light

24. Lights for vessels towing and pushing

A power driven vessel when towing must show

two masthead lights on top of each other, instead of the masthead(s) prescribed in Rule 23;

for a "long tow", three masthead lights on top of each other, instead of two, and a diamond shape.

sidelights;

a sternlight;

a towing light vertically above the sternlight;

if a pushing vessel and the vessel it is pushing are rigidly connected, they count together as a power driven vessel and must show the light prescribed by Rule 23.

If the pushing vessel and vessel being pushed are not rigidly connected, they must instead show:

two masthead lights on top of each other, instead of the masthead(s) prescribed in Rule 23;

sidelights;

a sternlight on the pushing vessel only.

Power driven vessels larger than 50 metres (164 ft) which are towing or pushing and are not part of a composite unit must also show:

a second masthead abaft of and higher than the forward one (vessels smaller than 50 metres may also show this light).

Vessels being towed that are not inconspicuous or partly submerged must show:

sidelights;

a sternlight;

a diamond shape if the tow is longer than 200 metres (656 ft).

Any number of vessels being towed or pushed together shall be lit as one vessel, and

a vessel being pushed ahead must show sidelights at its forward end if it is not part of a composite unit;

a vessel being towed alongside must show a sternlight and sidelights at its forward end.

A vessel being towed that is inconspicuous or partly submerged must show:

if it is narrower than 25 metres (82 ft), one all-round white light near the forward end (except if it is a dracone) and one near the after end;

if it is wider than 25 metres (82 ft), then also two all round white lights at the extremities of its breadth;

if it is longer than 100 metres (328 ft), then in a series of such all round white lights spaced no further than 100 metres (328 ft) apart;

a diamond shape near the end of the last vessel, and, if the tow is longer than 200 metres (656 ft), another diamond shape as far forward as possible.

If for any reason it is not possible to light the vessel according to these rules, all possible measures must be taken to light the vessel and indicate its presence.

If the towing vessel is not normally engaged in towing operations and it is impractical to light it correctly, it is not obliged to show these lights if it is towing a vessel in distress or in need of assistance. All possible measures must be taken to show that it is towing; in particular the towline should be illuminated.

(b) In a sailing vessel of less than 20 metres (66 ft) in length the lights prescribed in paragraph (a) of this Rule may be combined in one lantern carried at or near the top of the mast where it can best be seen.

(c) A sailing vessel underway may, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower green, but these lights shall not be exhibited in conjunction with the combined lantern permitted by paragraph (b) of this Rule.

(d) 1. A sailing vessel of less than 7 metres (23.0 ft) in length shall, if practicable, exhibit the lights prescribed in paragraph (a) or (b) of this Rule, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.

2. A vessel under oars may exhibit the lights prescribed in this Rule for sailing vessels, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.

(e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards.

26. Lights for fishing vessels

Fishing Vessels

(a) A vessel engaged in fishing, whether underway or at anchor, shall exhibit only the lights and shapes prescribed in this Rule.

(b) A vessel when engaged in trawling, by which is meant the dragging through the water of a dredge net or other apparatus used as a fishing appliance, shall exhibit:

two all-round lights in a vertical line, the upper being green and the lower white, or a shape consisting of two cones with their apexes together in a vertical line one above the other;

a masthead light abaft of and higher than the all-round green light; a vessel of less than 50 metres (164 ft) in length shall not be obliged to exhibit such a light but may do so;

when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.

(c) A vessel engaged in fishing, other than trawling, shall exhibit:

two all-round lights in a vertical line, the upper being red and the lower white, or a shape consisting of two cones with apexes together in a vertical line one above the other;

when there is outlying gear extending more than 150 metres horizontally from the vessel, an all-round white light or a cone apex upwards in the direction of the gear;

when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.

(d) The additional signals described in Annex II to these Regulations apply to a vessel engaged in fishing in close proximity to other vessels engaged in fishing.

(e) A vessel when not engaged in fishing shall not exhibit the lights or shapes prescribed in this Rule, but only those prescribed for a vessel of her length.

27. Lights for vessels not under command or restricted in their ability to manoeuvre

Vessels not under command or restricted in their ability to manoeuvre

(a) A vessel not under command shall exhibit:

1. two all-round red lights in a vertical line where they can best be seen;

2. two balls or similar shapes in a vertical line where they can best be seen;

3. when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.

(b) A vessel restricted in her ability to manoeuvre, except a vessel engaged in mine-clearance operations, shall exhibit:

three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;

three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond;

when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in sub-paragraph (i);

when at anchor, in addition to the lights or shapes prescribed in sub-paragraphs (i) and (ii), the light, lights or shape prescribed in Rule 30.

(c) A power-driven vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shall, in addition to the lights or shapes prescribed in Rule 24(a), exhibit the lights or shapes prescribed in sub-paragraphs (b)(i) and (ii) of this Rule.

(d) A vessel engaged in dredging or underwater operations, when restricted in her ability to manoeuvre, shall exhibit the lights and shapes prescribed in sub-paragraphs (b)(i), (ii) and (iii) of this Rule and shall in addition, when an obstruction exists, exhibit:

two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists;

two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass;

when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30.

(e) Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in paragraph (d) of this Rule, the following shall be exhibited:

three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;

a rigid replica of the International Code flag "A" not less than 1 metre (3.3 ft) in height. Measures shall be taken to ensure its all-round visibility.

(f) A vessel engaged in mine clearance operations shall in addition to the lights prescribed for a power-driven vessel in Rule 23 or to the lights or shape prescribed for a vessel at anchor in Rule 30 as appropriate, exhibit three all-round green lights or three balls. One of these lights or shapes shall be exhibited near the foremast head and one at each end of the fore yard. These lights or shapes indicate that it is dangerous for another vessel to approach within 1,000 metres (0.62 mi) of the mine clearance vessel.

(g) Vessels of less than 12 metres (39.4 ft) in length, except those engaged in diving operations, shall not be required to exhibit the lights and shapes prescribed in this Rule.

(h) The signals prescribed in this Rule are not signals of vessels in distress and requiring assistance. Such signals are contained in Annex IV to these Regulations.

28. Lights for vessels constrained by their draught

A vessel constrained by her draft may, in addition to the lights prescribed for power-driven vessels in Rule 23, exhibit where they can best be seen three all-round red lights in a vertical line, or a cylinder.

at or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red;

when underway, in addition, sidelights and a sternlight;

when at anchor, in addition to the lights prescribed in subparagraph (1), the light, lights, or shape prescribed in Rule 30 for vessels at anchor.

(b) A pilot vessel when not engaged on pilotage duty shall exhibit the lights or shapes prescribed for a similar vessel of her length.

30. Lights for vessels anchored and aground

A vessel at anchor must display an all-round white light or one black ball in the fore part and another all-round white light at or near the stern at a lower level than the light in the fore part. BUT if the vessel is less than 50 meters in length it may exhibit an all-round white light where it can best be seen instead of the lights foresaid.

Where it is impracticable for a seaplane or a WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in the Rules of the Part she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.

Vessels 12 metres (39.4 ft) or more in length should carry a whistle and a bell and vessels 100 metres (328 ft) or more in length should carry in addition a gong. On many vessels, a horn serves the purpose of a whistle.

Any vessel (or class of vessel) provided that she complies with the requirements of the International Regulations for the Preventing of Collisions at Sea, 1960, the keel of which is laid or is at a corresponding stage of construction before the entry into force of these Regulations may be exempted from compliance therewith as follows:

(a) The installation of lights with ranges prescribed in Rule 22, until 4 years after the date of entry into force of these regulations.

(b) The installation of lights with color specifications as prescribed in Section 7 of Annex I to these Regulations, until 4 years after the entry into force of these Regulations.

(c) The repositioning of lights as a result of conversion from Imperial to metric units and rounding off measurement figures, permanent exemption.

(d) (i) The repositioning of masthead lights on vessels of less than 150 meters in length, resulting from the prescriptions of Section 3 (a) of Annex I to these regulations, permanent exemption.

(ii). The repositioning of masthead lights on vessels of 150 meters or more in length, resulting from the prescriptions of Section 3 (a) of Annex I to these regulations, until 9 years after the date of entry into force of these Regulations.

(e) The repositioning of masthead lights resulting from the prescriptions of Section 2(b) of Annex I to these Regulations, until 9 years after the date of entry into force of these Regulations.

(f) The repositioning of sidelights resulting from the prescriptions of Section 2(g) and 3(b) of Annex I to these Regulations, until 9 years after the date of entry into force of these Regulations.

(g) The requirements for sound signal appliances prescribed in Annex II to these Regulations, until 9 years after the date of entry into force of these Regulations.

(h) The repositioning of all-round lights resulting from the prescription of Section 9(b) of Annex I to these Regulations, permanent exemption.

2. The use or exhibition of any of the foregoing signals except for the purpose of indicating distress and need of assistance and the use of other signals which may be confused with any of the above signals is prohibited.

3. Attention is drawn to the relevant sections of the International Code of Signals, the Merchant Ship Search and Rescue Manual, Annex III and the following signals;

(a) a piece of orange-coloured canvas with either a black square and circle or other appropriate symbol (for identification from the air);